In analog circuit design, it may be difficult to obtain precise voltages or measurements because analog components have many parameters that vary with process, temperature, and/or or power supplied. Therefore, one or more reference voltages for an integrated circuit may be generated from a bandgap reference voltage circuit. If, however, the bandgap reference voltage is not accurate due to variations in the power supplied or temperature, then all reference voltages derived from the bandgap reference voltage will also be inaccurate. This could induce substantial errors in the operation of the integrated circuit.
Accurate resistor values are also important in analog circuits for achieving precise current values. For example, if resistor values in A/D converters are inaccurate, then the voltage range associated with each of the bits of the A/D converter may be in error.
Current techniques for achieving more precise resistor values includes the use of lasers to trim a resistor after fabrication, in order to obtain a precise value for that resistor. For example, a film resistor may be fabricated with a lower resistance value than desired whereby a laser beam can be used to remove a portion of the film of the resistor thereby increasing its resistance and effectively “trimming” the resistor to precisely the desired value. However, such trimmed resistors may drift after trimming and such drifting can be accelerated by thermocycling.
Another technique for trimming element values in an integrated circuit by the use of multiple fusible link elements. However, such a technique consumes substantial area on the integrated circuit, and requires additional external pins.